Partially Dielectric-Filled SIW Configuration: Frequency Bandwidth and Impedance Matching to Microstrip Line

In this paper, a partially dielectric-filled substrate integrated waveguide (PDF-SIW) configuration is analyzed for the frequency bandwidth and impedance matching to microstrip line. The PDF-SIW configuration may be designed for wider frequency bandwidth of the dominant TE₁₀ mode comparing to the homogeneous SIW. It is demonstrated that the propagation constant values computed for the PDF-SIW and for the equivalent partially dielectric-filled rectangular waveguide (PDF- RW) are practically the same, if the PDF-RW width is corrected based on a formula which is usually used for the homogeneous waveguides. It is also shown that the technique used to realize the transition from the homogeneous SIW to the microstrip line may be applied to realize the PDF-SIW to microstrip line transition, too.

1. Introduction

Substrate integrated waveguides (SIWs) [1], [2] have been proposed as a solution to integrate waveguides using PCB technology. In this way, transmission media showing higher quality factors comparing to the transmission lines may be developed. Unfortunately, the losses in SIWs are higher than in the traditional hollow waveguides, due to the losses in the solid dielectric inside the SIW. In order to reduce the dielectric losses or/and to increase the frequency bandwidth of the TE₁₀ dominant mode, different partially dielectric-filled SIW (PDF-SIW) configurations have been analyzed [3]–[7]. Note that in order to realize the via-hole arrays which model the side walls of the SIW, the solid dielectric inside the SIW cannot be completely removed. Usually, the PDF-SIW is analyzed based on the equivalent partially dielectric- filled rectangular waveguide (PDF-RW) which has continuous metallic side walls. If the width of the equivalent PDF-RW is equal to the distance between the centers of the PDF-SIW via-hole arrays, the TE₁₀ cutoff frequencies of the two waveguides are slightly different.